全文获取类型
收费全文 | 7816篇 |
免费 | 435篇 |
国内免费 | 56篇 |
专业分类
耳鼻咽喉 | 84篇 |
儿科学 | 156篇 |
妇产科学 | 191篇 |
基础医学 | 1071篇 |
口腔科学 | 134篇 |
临床医学 | 632篇 |
内科学 | 2097篇 |
皮肤病学 | 203篇 |
神经病学 | 599篇 |
特种医学 | 154篇 |
外科学 | 1170篇 |
综合类 | 45篇 |
一般理论 | 5篇 |
预防医学 | 599篇 |
眼科学 | 89篇 |
药学 | 504篇 |
中国医学 | 40篇 |
肿瘤学 | 534篇 |
出版年
2023年 | 44篇 |
2022年 | 86篇 |
2021年 | 211篇 |
2020年 | 90篇 |
2019年 | 138篇 |
2018年 | 173篇 |
2017年 | 132篇 |
2016年 | 121篇 |
2015年 | 159篇 |
2014年 | 232篇 |
2013年 | 291篇 |
2012年 | 554篇 |
2011年 | 623篇 |
2010年 | 289篇 |
2009年 | 303篇 |
2008年 | 610篇 |
2007年 | 617篇 |
2006年 | 606篇 |
2005年 | 581篇 |
2004年 | 516篇 |
2003年 | 453篇 |
2002年 | 414篇 |
2001年 | 70篇 |
2000年 | 64篇 |
1999年 | 80篇 |
1998年 | 65篇 |
1997年 | 69篇 |
1996年 | 42篇 |
1995年 | 39篇 |
1994年 | 37篇 |
1993年 | 35篇 |
1992年 | 44篇 |
1991年 | 42篇 |
1990年 | 44篇 |
1989年 | 47篇 |
1988年 | 30篇 |
1987年 | 26篇 |
1986年 | 28篇 |
1985年 | 43篇 |
1984年 | 22篇 |
1983年 | 21篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 14篇 |
1974年 | 17篇 |
1973年 | 14篇 |
1970年 | 12篇 |
排序方式: 共有8307条查询结果,搜索用时 46 毫秒
71.
Luis C. Antn Sol Ruiz Elena Barrio Guillermo Marqus Angel Snchez Fernando Vivanco 《European journal of immunology》1994,24(3):599-604
The covalent binding reaction of the third component of complement (C3) with rabbit IgG immune aggregates has been studied by enzymic digestion of C3b-IgG adducts. In these adducts C3b was radioactively labeled in the free thiol group generated during activation of the internal thioester of C3. Trypsin digestion of 14C-labeled C3b-IgG adducts degrades C3b to a small antibody-bound 14C-labeled C3 fragment (14C-C3frg), whereas the antibody remains unaltered. Papain digestion of trypsin-treated 14C-C3frg-IgG complexes generated Fc and Fab fragments bearing equivalent amounts of covalently bound 14C-C3frg (43% and 40%, of the total C3 present in the aggregates, respectively). Hydroxylamine treatment of the 14C-C3frg-Fab and 14C-C3frg-Fc complexes released a 14C-C3frg of similar size (about 3–4 kDa) in which the N-terminal residue was the radiolabeled Cys1010. A fragment with the same radioactive N terminus and characteristics was obtained by sequential trypsin and papain digestion of purified C3 labeled with iodo–[14C] acetamide. Affinity-purified 14C-C3frg-Fc complexes digested with pepsin generated a mixture of radioactive peptides, most probably complexes formed by 14C-C3frg and Cγ2 or the hinge digestion products, and 14C-C3frg-pFc' complexes. The latter was also immunoprecipitated with anti-Fc-Sepharose from the pepsin digestion supernatants of 14C-labeled-C3b-IgG complexes. Taken together these data indicate that, during complement activation through the alternative pathway by IgG immune aggregates, C3 is not bound to a single site on the antibody molecule. Both Fab and Fc regions of IgG are equally efficient targets for C3 anchorage. In addition, the data confirm the pFc' as a region of C3 attachment within the Fc portion, and strongly suggest that C3b is bound either to the Cγ2 domain or the hinge or both. 相似文献
72.
Paredes AM Ferreira D Horton M Saad A Tsuruta H Johnston R Klimstra W Ryman K Hernandez R Chiu W Brown DT 《Virology》2004,324(2):373-386
Alphaviruses have the ability to induce cell-cell fusion after exposure to acid pH. This observation has served as an article of proof that these membrane-containing viruses infect cells by fusion of the virus membrane with a host cell membrane upon exposure to acid pH after incorporation into a cell endosome. We have investigated the requirements for the induction of virus-mediated, low pH-induced cell-cell fusion and cell-virus fusion. We have correlated the pH requirements for this process to structural changes they produce in the virus by electron cryo-microscopy. We found that exposure to acid pH was required to establish conditions for membrane fusion but that membrane fusion did not occur until return to neutral pH. Electron cryo-microscopy revealed dramatic changes in the structure of the virion as it was moved to acid pH and then returned to neutral pH. None of these treatments resulted in the disassembly of the virus protein icosahedral shell that is a requisite for the process of virus membrane-cell membrane fusion. The appearance of a prominent protruding structure upon exposure to acid pH and its disappearance upon return to neutral pH suggested that the production of a "pore"-like structure at the fivefold axis may facilitate cell penetration as has been proposed for polio (J. Virol. 74 (2000) 1342) and human rhino virus (Mol. Cell 10 (2002) 317). This transient structural change also provided an explanation for how membrane fusion occurs after return to neutral pH. Examination of virus-cell complexes at neutral pH supported the contention that infection occurs at the cell surface at neutral pH by the production of a virus structure that breaches the plasma membrane bilayer. These data suggest an alternative route of infection for Sindbis virus that occurs by a process that does not involve membrane fusion and does not require disassembly of the virus protein shell. 相似文献
73.
74.
Villalba-Caloca J García-García Mde L Sifuentes-Osornio J Sada-Díaz E Salazar-Lezama MA 《Gaceta médica de México》2003,139(5):471-492
Tuberculosis is a public health problem. If the current trends continue, is expected to arrive to 10.2 million of new cases in 2005. There are three studies accomplished in 1995 in Mexican patients. The results show important difficulty in the application and the follow-up of the program of control of the tuberculosis, what has caused accumulation of chronic cases, moderate rate of primary resistance and alarming levels of primary and secondary multiresistance (23%). Mechanism of protective immunity against mycobacterium tuberculosis (MTB) in humans have not been clarified. Different subpopulations of lymphocytes CD4, CD8 and other populations as well as macrophages, and monocytes, have an important role. In industrialized countries, the managing of the MDRTB is based on the use of individualized treatments with second line drugs according to susceptibility test, however the foregoing has not been possible to apply it middle or low income countries. WHO has launches the initiative "DOTS plus" that consist in the administration of a standarized regimen on the basis of epidemiology of resistance in the country or region. 相似文献
75.
Benavides F Zamisch M Flores M Campbell MR Andrew SE Angel JM Licchesi J Sternik G Richie ER Conti CJ 《Genes, chromosomes & cancer》2002,35(4):299-310
Genomic instability is believed to play a significant role in cancer development by facilitating tumor progression and tumor heterogeneity. Inter-simple sequence repeat (inter-SSR) PCR has been proved to be a fast and reproducible technique for quantitation of genomic instability (amplifications, deletions, translocations, and insertions) in human sporadic tumors. However, the use of inter-SSR PCR in animal models of cancer has never been described. This new technique has been adapted in our laboratory for the analysis of spontaneous and induced mouse tumors. We established the best PCR conditions for each microsatellite-anchored primer and critically evaluated the reproducibility of the band patterns. We also studied the variation of the fingerprints between and within various inbred mouse strains, including wild-derived lines. Tumor-specific alterations were detected as gains, losses, or intensity changes in bands when compared with matched normal DNA. We quantitated the extent of alterations by dividing the number of altered bands in the tumor by the total number of bands in normal DNA (instability index). By means of inter-SSR PCR, we successfully analyzed genomic alterations in various mouse tumors, including spontaneous thymic lymphomas developed in Msh2 knockout mice as well as chemically induced squamous cell carcinomas and thymic lymphomas. Instability index values ranged between 0 and 9%, the highest levels observed in N-methyl-N-nitrosourea-induced thymic lymphomas generated in Trp53 (p53) nullizygote (-/-) mice. We report here, for the first time, the use of inter-SSR PCR to detect somatic mutations in mouse tumoral DNA, including laser-capture microdissected, methanol-fixed tissues. These PCR-based fingerprints provide a novel approach to assessing the number and onset of mutational events in mouse tumors and will help to understand better the mechanisms of carcinogenesis in mouse models. 相似文献
76.
Pérez C Tous M Gallego S Zala N Rabinovich O Garbiero S Martínez MJ Cunha AM Camino S Cámara A Costa SC Larrondo M Francalancia V Landreau F Bartomioli MA 《Journal of medical virology》2004,72(4):661-667
Human herpesvirus-8 (HHV-8) causes Kaposi's sarcoma (KS) and lymphoproliferative disorders in both HIV-infected and uninfected patients. HHV-8 has a worldwide occurrence but infection rates vary according to a combination of geographic and behavioral risks. The main transmission route seems to be sexual, nevertheless, nasal secretions, saliva, blood, and organ graft have been proposed. HHV-8 was postulated as a new infectious agent for screening in blood donors. The aim of this study was to evaluate the prevalence of antibodies against HHV-8 antigens in blood donors of South America. Serum samples from 2,470 blood donors from Argentina, Brazil, and Chile corresponding to five geographic regions were studied by indirect immunofluorescence assay (IFA). Seroprevalence rate was 3.7% (92/2,470; 95% CI 2.9-4.5) in the entire blood donor population distributed as follows: Argentina, 4.0% (Buenos Aires city, 4.3%; Bahia Blanca, 2.4%; and Córdoba, 4.0%), Campinas (Brazil), 2.8%; and Santiago de Chile, 3.0%. There was no difference (P>0.05) between men and women or age related, except in Brazil where positive cases were 30-49-year-old males. The present study, which includes different geographical areas of multiple countries from South America, has not been done before. The results show similar prevalence rates among the studied zones corresponding to low-prevalence regions. South America is a large sub-continent with a wide spectrum of population and geographical characteristics, thus, more HHV-8 prevalence studies should be necessary to establish possible regional differences. 相似文献
77.
Angel González-Sistal M.D. Ph.D. Alicia Baltasar Sánchez M.D. 《Journal of digital imaging》2006,19(3):270-275
Purpose This study was conducted to evaluate the diagnostic usefulness of gray level parameters in order to distinguish healthy bone
from osteoblastic metastases on digitized radiographs.
Materials and methods Skeletal radiographs of healthy bone (n = 144) and osteoblastic metastases (n = 35) were digitized using pixels 0.175 mm in size and 4,096 gray levels. We obtained an optimized healthy bone classification
to compare with pathological bone: cortical, trabecular, and flat bone. The osteoblastic metastases (OM) were classified in
nonflat and flat bone. These radiological images were analyzed by using a computerized method. The parameters (gray scale)
calculated were: mean, standard deviation, and coefficient of variation (MGL, SDGL, and CVGL, respectively) based on gray
level histogram analysis. Diagnostic utility was quantified by measurement of parameters on healthy and pathological bone,
yielding quantification of area under the receiver operating characteristic (ROC) curve, AUC.
Results All three image parameters showed high and significant values of AUC when comparing healthy trabecular bone and nonflat bone
OM, showing MGL the best discriminatory ability (0.97). As for flat bones, MGL showed no ability to distinguish between healthy
and flat bone OM (0.50). This could be achieved by using SDGL or CVGL, with both showing a similar diagnostic ability (0.85
and 0.83, respectively).
Conclusion Our results show that the use of gray level parameters quantify healthy bone and osteoblastic metastases zones on digitized
radiographs. This may be helpful as a complementary method for differential diagnosis. Moreover, our method will allow us
to study the evolution of osteoblastic metastases under medical treatment. 相似文献
78.
Marta Tojo Raquel Perez-Becerra Angel Vazquez-Boquete Arancha García-Rivero Tomas García-Caballero Jeronimo Forteza Maximo Fraga 《Diagnostic molecular pathology》2008,17(1):59-63
Fluorescence in situ hybridization (FISH) is a useful cytogenetic technique for the detection of chromosome aberrations. However, applying this technique routinely on paraffin-embedded tissue is hampered by technical problems. The efficiency of hybridization is influenced by formalin fixation time, and this may vary considerably between specimens. We present a simple method for improving hybridization by microscopically monitoring the time of enzymatic digestion. To establish optimal digestion time, enzymatic digestion was stopped at 3-minute intervals for biopsies and 10-minute intervals for autopsies in 24 paraffin-embedded samples. At every stop, tissue morphology was examined under light microscopy to determine if observed changes could be correlated with subsequent FISH results. The appearance of fernlike formations was found to mark the optimal digestion time that produced the strongest hybridization signals. Using this method of digestion time control, an additional 41 cases were evaluated for FISH with various types of probe. Monitoring under the microscope could be more spaced if the morphology did not change after the first visual control and could be adapted to the type of sample (in general, endoscopic samples, total digestion time of about 10 min; routine biopsies, 15 to 30 min; autopsy samples, 20 to 40 min). In every case, the appearance of the fernlike pattern correlated with proper hybridization signal. Monitoring digestion time for the appearance of fernlike structures is a useful method for improving reproducibility of FISH technique on paraffin-embedded samples. It is particularly useful when dealing with samples under heterogeneous fixation conditions (consultations, autopsies, etc.), because it eliminates the need for repetition. 相似文献
79.
The 505 amino acid L1 protein of the human papillomavirus type 11 (HPV 11) is the major capsid polypeptide that has been shown to self-assemble into virus-like particles (VLPs) in vivo and in vitro. While L1 is essential for viral infection, expression studies in mammalian cells have been hampered by different codon preference between the virus and its host. To optimize L1 gene expression in mammalian cells, we converted wild-type HPV 11 L1 (11 L1wt) codons to those more common in human genes. The modified HPV 11 L1 gene (11 L1h) generated protein levels that were at least 100-fold higher than those of wild-type HPV 11 L1, while no obvious differences were seen in the level of mRNA. HPV 11 L1 protein was detected in mammalian epithelial and fibroblast cells, by immunoblotting and indirect immunofluorescence (IIF) techniques. Unlike the situation in situ, IIF revealed the presence of L1 mainly at perinuclear sites. Virus-like particles assembled intranuclearly only to a low extent, as indicated by transmission electron microscopy. DNA vaccination using the HPV 11 L1h gene yielded a drastic increase in L1-specific antibody production in mice as compared to immunization with the wild-type gene. 相似文献
80.
Leone PE Vega ME Jervis P Pestaña A Alonso J Paz-y-Miño C 《Journal of human genetics》2003,48(12):639-641
RB1 is the gene responsible for retinoblastoma, the most common malignant intraocular tumor of infancy and early childhood. There are no reports about this gene in Ecuadorian populations, and only a few studies have been published in Latin America about this subject. There is a spectrum of more than 370 mutations described in the RB1 gene mutation database (http://www.d-lohmann.de/Rb/mutations.html), and alterations have been found in 25 of the 27 exons. During the exon-by-exon analysis of 31 tumor and blood samples from Ecuadorian patients, we found two new mutations and three novel polymorphisms. One of the polymorphisms is located in intron 26 where no alterations of the gene have been described previously. The polymorphisms were found in all of the patients tumor samples, but not in normal population, suggesting there might be a relationship between these polymorphisms and the development of retinoblastoma in the Ecuadorian population.The nucleotide sequence data reported are available in the GenBank database under the accession numbers: AY243567, AY260472, AY260473, AY273783 相似文献